This invention relates generally to water treatment systems and methods and, more particularly, to systems and methods for treating ship ballast water to eliminate non-indigenous marine animals in the ballast water.
Global shipping moves 80 percent of world commodities. When ships load and/or remove their cargo, it is necessary to counteract the weight imbalance with ballast water in order for the ship to load and travel safely. In addition to maintaining a ship""s weight balance and stability, ballast water is carried by ships to adjust a vessel""s trim for optimal steering, propulsion, and safety. Ballasting fulfills many other functions including: reducing stresses on the hull of the ship, providing for transverse stability, aiding propulsion by controlling the submergence of the propeller, assisting maneuverability by submerging the rudder and reducing the amount of exposed hull surface (freeboard or windage), and compensating for weight lost from fuel and water consumption. (Stemming the Tide: Controlling Introductions of non-indigenous Species by Ship""s Ballast Water, 1996). The use of ballast water varies among vessel types, among port systems, and according to cargo and sea conditions. Ballast water often originates from ports and other coastal regions, which are rich in planktonic and other organisms. It is variously released at sea, along coastlines, and in port systems. As a result, a diverse mix of non-native or exotic organisms is transported and released around the world with the ballast water of ships.
Generally, many of the species of organisms contained in ballast water are either non-native or potentially pathogenic when they are released into the receiving water of the port. The transfer of organisms in ballast water has resulted in the unintentional introduction of tens to hundreds of nonindigenous freshwater and marine species to ports around the world. The invasion of these non-indigenous aquatic organisms has had tremendous detrimental impacts on native ecosystems and continues to cost billions of dollars in remedial actions. For example, the ballast-mediated introduction of the zebra mussel in the U.S. Great Lakes during the 1980s is expected to cost that region over $5 billion. Other examples include the introduction of toxic dinoflagellates in Australia and that of the Asian claim (Potamocorbula Amurensis) in the San Francisco Bay-Delta region. According to the U.S. Coast Guard, xe2x80x9c . . . ballast water from ships is one of the largest pathways for the intercontinental introduction and spread of aquatic nuisance species.xe2x80x9d (http://www.uscg.mil/hq/g-m/mso/mso4/bwm.html, July 2000).
Ballast water amounts are extremely large, especially for non-cargo ships. For example, large tankers can carry in excess of 200,000 m3 of ballast water and rates of pumping can be as high as 15,000 to 20,000 m3/h. It is estimated that more than 3,000 species of plants and animals are transported daily in ballast water. (Office of Technology Assessment, 1993). The most common plants carried in ballast water are phytoplankton, especially diatoms and dinoflagellates, and floating detached plants, including seaweed (algae) and seagrasses (eelgrass or turtlegrass). Zooplankton found in ballast is diverse and dense.
Differences in volume are due to available data used in the calculations.
Presently, open ocean ballast water exchange (BWE) is the only method in use for reducing exotic introductions via ballast water. Ballast water exchange involves replacing coastal water with open-ocean water that is located at least 200 miles offshore during a voyage. This process may reduce the density of coastal organisms in ballast tanks that may be able to invade a recipient port, replacing them with oceanic organisms with a lower probability of survival in nearshore waters.
Ballast water exchange is recommended as a voluntary measure by the International Maritime Organization (IMO). In addition, the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990 (P.L. 101-646) required that all vessels entering Great Lakes Ports from beyond the exclusive economic zone (EEZxe2x80x94out to 200 miles from shore) undergo ballast exchange or some comparably effective ballast treatment which conforms to discharge requirements of the Federal Water Pollution Control Act (33 U.S.C. 1251). These requirements were extended to vessels arriving in ports of the upper Hudson River, north of the George Washington Bridge on Nov. 4, 1992, and now apply to all vessels entering U.S. waters.
The National Invasive Species Act (NISA) of 1996 (P.L. 104-332) reauthorized and amended the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990. NISA issued mandatory ballast management reporting and voluntary ballast exchange guidelines to all vessels that enter U.S. waters from outside the EEZ, with the exception of military vessels, crude oil tankers that carry out coastwise trade, and some passenger ships that are equipped with ballast water treatment systems.
There are two approved methods of open-ocean exchange: empty/refill and flow through. The empty/refill method consists of the ballast tanks being emptied and subsequently refilled. This process compromises the stability of the ship; therefore ships traveling in rough seas will not be able to use this method. Stability can be managed more easily with ships that have a higher number of small volume ballast tanks, rather than a low number of large volume ballast tanks, although the ability to safely conduct ballast water exchange still depends upon weather and sea surface conditions. The flow through method consists of pumping ballast water (three times the capacity of the ballast tank) through the tanks, allowing it to overflow through air vents of deck hatches. Stability is less of an issue during this process, but the integrity of the ship is still compromised. Additional safety hazards associated with this method include potential tank over pressurization and water overflowing on the deck. Thus, it is not always possible to perform an exchange. Furthermore, both of the approved ballast water exchange methods only reduce the density of coastal organisms in ballast tanks following an exchange. There are still some residual coastal organisms in the tanks, so these methods are only partly effective.
The exchange efficiency for both methods has been estimated to range from 75-95 percent in a variety of studies on specific biological species, usually depending on the structure of the ballast tanks (e.g., placement of intake and outflow pipes, shape of tanks, size of baffles in tanks, etc.). Although open-ocean exchange significantly reduces the risk of invasion, the remaining 5-25 percent still posses a significant threat. Another disadvantage is that open-ocean exchange cannot be achieved during coastal voyages, where the ship never leaves the EEZ.
An alternative to open-ocean exchange is ballast water treatment, where organisms in the water are killed or removed from the ballast water. An effective ballast water treatment system must meet the following criteria: it must be practical for mariners to operate, safe for mariners and the ship, easy to monitor, cost effective, biologically effective and have a minimal environmental impact (i.e. not discharging toxic chemical byproducts). Until now, it has been challenging for researchers to come up with a system that meets the all of these criteria.
Treatment of ballast water can take place during uptake, in transit (in the ballast tank), during discharge, or on a mobile or onshore treatment system/plant. There are many different options that are being explored today including filtration, UV irradiation, hydrocyclonic separation, thermal treatment, biocides, and more. Many projects are pairing two different kinds of treatment technologies (i.e. filtration and UV) to gain a higher efficiency across all taxonomic groups of organisms.
The current treatment approaches that are being explored suffer a variety of flaws. Most of them have no techniques available for routine analysis to determine effectiveness. Additionally, approaches like filtration will be impacted by oil and particulates and by the need for the disposal of the backwash stream (presumably back into the harbor where the ballasting is being done but it is uncertain how this concern would be addressed). Oil would rapidly clog any kind of filtration device. The more sophisticated approaches involving the use of ultra violet (UV) irradiation will also be immediately impacted and likely shut down by the oil and rendered ineffective by particulates. Non-degradable biocides seem to offer very little hope in this application due to the potential toxicity of the discharge.
Therefore, there exists a need for a more effective system for managing ballast water. This system must be practical for mariners to operate, safe for mariners and the ship, easy to monitor and analyze, cost effective, biologically effective and have a minimal environmental impact.
This invention provides systems and methods for treating ballast water to effectively and economically annihilate non-indigenous marine animals in the ballast water. In the preferred embodiment, sufficient amounts of a killing agent and a reducing agent are added sequentially and separately to a ballast water container. A killing agent, such as a chloramine, rapidly annihilates most or all of the non-indigenous macro and micro-organisms in the ballast water. The subsequent addition of the reducing agent transforms the toxic chloramine into non-toxic by-products, and creates an anoxic environment wherein any remaining organisms, which, although highly unlikely, could possibly have survived the chloraminesare, are exposed to conditions that cannot support life. Suitable reducing agents include solid-state agents such as activated carbon and liquid chemical reducing agents, such as sodium thiosulfate, sodium sulfite, sodium dithionite, sodium bisulfite, or sulfur dioxide. Preferably, oxygen is added subsequent to the addition of the reducing agent to remove any excess reducing agent and to provide dissolved oxygen for aquatic species in the receiving water. In all embodiments, treatment of the ballast water can take place during uptake, in transit in the ballast container, immediately before or during discharge, or on a mobile or onshore treatment system or plant, and can be accomplished either automatically or manually.
The treatment system can either be ship board mounted or mounted on a barge which is brought next to the ship for treatment, depending upon the degree of treatment needed and the volume of ballast water requiring treatment. The concentration or residual of the killing agent, the reducing agent, and the oxygen can be easily monitored with low cost devices such as hand-held Hach kits or simple swimming pool analyzers.